The long-term goal of this research is to investigate the effects of aging on the regulation of cutaneous blood flow. The specific objectives of this project are: 1) to determine the relative effects of aging on blood flow in the superficial dermal capillaries and total cutaneous regional blood flow; 2) to test various hypotheses related to the decrease in single capillary blood flow previously observed in the dermal region of elderly male subjects; 3) to test the hypothesis that the ability of dermal capillary blood flow to respond to changes in environmental temperature is decreased with age; 4) to determine if previously observed changes in cutaneous blood flow with age are attenuated in elderly who participate in regular physical exercise; and 5) to determine if females differ from males with regard to the affects of age on cutaneous blood flow. The data for this study will be obtained by way of a cross-sectional comparison of blood flow velocity in individual cutaneous capillaries of human subjects within the following age groups: 20-35 yr; 35-50; 50-65; 65-80. All subjects will be nonusers of tobacco products, non-diabetic, have normal plasma lipid concentration and will be matched in accordance to general health and level of resting blood pressure. Blood flow in single capillaries within the nailfold skin of the toe will be measured via TV microscopy at rest and in response to the following physiological perturbations: changes in arterial pressure; temperature change and ischemia. In addition, metatarsal artery blood flow velocity and total toe blood flow will be measured respectively via doppler ultrasound and plethysmography. These measurements will be matched with simultaneous measurements of capillary blood flow to investigate age-related changes in the relationship between macro and microcirculatiory flow in the skin.